Threaded pipe connection with improved seal

ABSTRACT

An improved coupling for joining together threaded tubular sections is disclosed. The coupling includes a seal seat between the threaded areas of the coupling and a seal assembly positioned on the seal seat. The seal assembly engages the end of the threaded tubular section and forms an axial seal without application of radial stress in the coupling. The seal assembly has an elastomeric component and a rigid component.

BACKGROUND OF INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates generally to threaded connectionsfor joining sections of tubing, casing, line pipe or other tubularsections forming long strings of pipe used in drilling and producing oiland gas. More particularly, the invention relates to a threadedconnection having a sealing mechanism for maintaining leak resistanceagainst liquid and gas pressures.

[0003] 2. Description of Related Art

[0004] In the search for oil and gas reserves, major oil companies haveincreasingly moved to deep water drilling environments. Early success indeep water has demonstrated the existence of large, commercially viableoil and gas fields. Technological advancements now permit routinedrilling in deeper offshore waters and even further below the sea floorthan just 5 years ago. Deeper drilling is also more common in onshorewells. However, the deep-water drilling environment and deeper wellshave presented new industry challenges that make these endeavors bothrisky and expensive. High rig costs have generated demands for tubularconnections that assemble quickly with positive make-up indication toreduce the time for running an entire tubular string.

[0005] Tubular strings used for drilling and production of oil and gasconsist of individual sections commonly 40-ft in length. However, someoperators use specially rolled tubulars up to 60-ft in length to reducethe number of connections in a string thereby reducing overall stringcosts. Manufacturing, transportation, and handling constraints limit themaximum practical length of individual tubular sections.

[0006] Oil and gas wells consist of a series of tubular strings. Largediameter tubulars are installed near the surface or sea floor andsuccessively smaller diameter tubular strings telescope inside until thetarget depth is attained. Internal and external (collapse) pressuresincrease with depth and smaller diameter tubulars have higher resistanceto these loads. Thus, all tubular sections have setting depth limitsbased on diameter to thickness ratios and material strength properties.In general, smaller diameter tubulars can be set to greater depths.

[0007] Tubular strings are designated as drive, conductor, surface,intermediate, protective, liner and/or production tubulars. Stringscommonly known as tubing are the conduits through which oil and gasactually flows to the surface. Those skilled in oil and gas drilling andproduction understand the application behind each of these tubulardesignations.

[0008] Tubular sections are prepared for running with connections ateach end. One end, known as the pin end, is externally threaded. Theother end is internally threaded and is known as the box end. The boxend may be internally threaded onto the tubular section or, the tubularsection may be externally threaded with an internally threaded couplingscrewed onto the end.

[0009] On the rig, each tubular section is raised in the derrick,lowered below the deck and held at the floor with an internally threadedmember facing up. The next tubular section is raised into the derrickand stabbed into the waiting internally threaded member. Aftersuccessful stabbing, the two tubular sections are screwed together. Allassembled tubular sections are then lowered in preparation for the nexttubular section. The process continues, one tubular section at a time,until the string reaches the target setting depth.

[0010] The standard methods of joining lengths of tubular sections areby either threaded and coupled or integral joint connections. Threadedand coupled connections use a coupling that is a short, tubular piece,usually consisting of the same material as the tubular section. Integraljoint connections, also known as flush or super flush, are machineddirectly on the tubular section and do not require a coupling. Theseintegral joint connections are often used when annular clearance betweensuccessive riser strings is reduced, and/or there is restricted wellboreclearance that is anticipated to cause problems in reaching the desiredsetting depth. While integral joint connections are useful in restrictedwellbore clearance situations and have demonstrated good performanceresisting high pressure, all have relatively low axial tensionresistance. Installation of integral joint connections follows the samebasic procedures as threaded and coupled connections.

[0011] Threaded couplings often are assembled with various types oflubricants commonly referred to as thread compounds or pipe dope. Inconnections that shoulder out, excess thread compound trapped within thethreads can exert significant hydraulic pressure in mating threadelements. Such hydraulic pressure can impart additional hoop stressesthat may degrade connection performance.

[0012] The oil industry, through the American Petroleum Institute, hasstandardized sizes, weights and material grades of tubular sections andconnections, as set forth in American Petroleum Institute SpecificationStandards 5B and 5CT. Through standardization, a worldwide serviceinfrastructure has evolved for the manufacture and use of these tubularproducts. Economies of scale through standardization have provided: (a)low-cost, worldwide supplies, (b) universal inspection and measurementmethods, (c) standard gauges and handling tools, and (d) readilyavailable accessories. Connections for joining tubular sections of thesame size and weight are completely interchangeable. Further, thereexists a set of standard assembly procedures for use in the field asdescribed in American Petroleum Institute Recommended Practice 5C1.

[0013] Proper make-up of industry standard API threaded couplings occurswhen the coupling, or box member, covers a reference mark on the pinmember, which generally consists of a ⅜-in. equilateral triangle diestamp or other similar impression on the pin member. Due to allowablethread tolerances, however, variability exists in the make-up. As aresult, the box member's position at proper make-up is not always thesame relative to the mark on the pin member. For example, if the boxmember is machined on the small side of the allowable tolerance band andthe mating pin member is machined on the large side of the allowabletolerance band, proper make-up occurs when the coupling covers the baseof the triangle stamp. At another tolerance extreme, a connection with alarge box and a small pin would make up when the coupling reaches theapex and covers most (or all) of the triangle stamp. The range oftolerances of the pin and box members causes considerable uncertainty byrig personnel trying to determine whether connections are properlyassembled.

[0014] Standard API threaded connections use a thread interferencesealing mechanism. Interference develops when an externally threaded pinmember is screwed into an internally threaded box member. The OD of thepin is slightly larger than the ID of the box. As the two members arejoined, the box deflects outward and the pin deflects inward as the twomembers attempt to occupy the same space. The amount of relativedeflection of the two members is a function of the cross-sectionalbalance between the pin and box. Interference equals the difference ofbox deflection and pin deflection. Since both members are threaded on ataper, interference is also a function of axial advancement of the pininto the box.

[0015] Standard API threaded connections also have demonstratedunsatisfactory field performance in both normal and critical wells. Ahistory of leaks in casing strings with Standard API connections atpressures around 4,000 psi to 5,000 psi has resulted in a general lackof confidence in thread interference seals by the industry. Some of theother problems with these connections include difficult stabbing duringmake-up (common with large outer diameter tubular products), threaddamage (or galling) when disassembled in the field, and string parting.Each of these problems results in significant repair and operatingcosts. In-service failures are potentially hazardous to the environmentand pose serious safety risks to onsite personnel.

[0016] Efforts to improve stabbing and reduce thread galling haveincluded modifications to the thread form, special thread surfacetreatments including abrasive blasting and application of anti-gallingagents. String parting has been addressed by structurally enhancing thecoupling body or through the use of specially designed “hook” typethreads. While these approaches have abandoned the industry standardthread form, connections with these features are commonly used to avoidthese common problems.

[0017] Efforts to solve the leak problem have included modified threadforms, elastomeric seals, metal-to-metal seals, and a combination ofspecial tolerances and make-up procedures. Some designs haveincorporated one or more of these approaches and claim to have multiple,redundant sealing mechanisms for enhanced connection performance.However, these approaches are often expensive and impractical becausethey abandon use of industry standard thread forms and/or requirespecial accessory equipment, handling and assembly procedures, and otheroperational changes.

[0018] Deviations from standard API thread forms are typically noteconomical because they fail to take advantage of the worldwideinfrastructure for service, interchangeability, handling andaccessories. Additionally, alternate connections require speciallythreaded accessory items that require extra logistics and significantadditional cost. In general, the industry will readily embrace anyconnection that meets the required performance criteria while allowingthe use of the industry standard thread form.

[0019] In the past, elastomeric seals have been used within matingthread elements of various connections used to join threaded tubularsections. Additionally, various other seals that impart additionalradial hoop stresses in the box member when energized also have beenused. As a result of added hoop stresses from the seals, theseconnections have performance disadvantages. Added radial hoop stressescan ultimately cause unexpected connection failure.

[0020] Metal-to-metal sealing mechanisms consist of axial and/or radialsealing surfaces. These seals rely on finely machined surfaces anddevelopment of high bearing (contact) pressure between mating sealingelements. While metal-to-metal seal connections have been successful inpractice, they require a high degree of care in manufacture, qualityassurance/control, handling and assembly. The use of special equipmentand personnel is also required to ensure proper assembly in preparationfor shipping offshore and for assembly at the rig. Additionalrequirements in all stages of tubular production result in highermanufacturing reject rates when compared with API Connections. Theseconnections require more personnel, inspection, equipment, and rig timefor installation in the well. As a result, these connections addsignificant cost when so-equipped tubular strings are purchased due toincreased inspections, specialty accessory equipment, personnel andrunning tools, and rig time.

[0021] The use of special tolerances and make-up procedures has gainedfavor in the industry for improved performance of API connections. Forexample, the connection described in U.S. Pat. No. 4,962,579 seeks toensure enhanced leak resistance by using a registry mark that, uponproper make-up, is visually inspected to be within the proper position.Other approaches include: (a) applying heavy surface plating (consistingof various soft, malleable metals) on internal threads for enhancedlubricity to protect the base metal and seal-ability; (b) assemblingwith specially formulated lubricants; and (c) special assemblyprocedures.

[0022] These alternatives have been successful in achieving enhancedconnection performance for somewhat greater cost when compared withstandard API connections. However, these alternative approaches arelimited to certain tubular wall thicknesses. Standard oilfield tubularsinclude many wall thickness options for any given outer diametertubulars section. As a result, couplings may be weaker than the pipesections in the string due to decreased wall thickness of the coupling.

[0023] Another effort to solve these problems has focussed on couplingdesign using the standard API threads. For example, U.S. Pat. No.5,015,017 to George B. Geary assigned to GB Tubulars of Houston, Tex.,discloses a threaded tubular coupling having an increased internal crosssection in the center of the coupling. The increased cross sectionimproves leak resistance by resisting expansion of the coupling due tointernal pressure, without increasing the outer diameter of thecoupling. The connection of U.S. Pat. No. 5,015,017 helps prevent lossof contact pressure in the threads between the pin and box members.

[0024] An increased cross section in the coupling center providessignificant hoop reinforcement in the coupling of U.S. Pat. No.5,015,017. Thus, it will better resist inward compression from chuckingduring assembly and outward expansion due to assembly, pressure or otherloads. Because the reinforced cross-section resists outward expansion ofthe coupling, more torque is required to achieve final make-up positionthan is required with a standard API coupling without the reinforcedcenter section. The increased torque required for make up of thecoupling of U.S. Pat. No. 5,015,017 causes increased friction in matingthread elements. As a result of the increased friction, the soft,malleable metallic plating moves more efficiently to better fill anyvoids in the mating thread elements to enhance thread form seal-ability.

[0025] A significant advantage of the connection described in U.S. Pat.No. 5,015,017 is its use of standard API thread forms. The connectionprovides enhanced performance and industry utility in a cost-effectiveconnection. Another advantage of the coupling described in U.S. Pat. No.5,015,017, is that the outside diameter can be smaller to allow use intight, downhole clearance situations. Because of the centerreinforcement, the connection maintains leak resistance exceeding thatof the tubular section and the connection is significantly more tensileefficient than flush joint connections.

[0026] The connections described in U.S. Pat. No. 5,015,017 have beensuccessful throughout the industry because it solves many of theproblems associated with Standard API connections and takes advantage ofthe worldwide infrastructure for service, interchangeability, handlingand accessories. However,-operators have been reluctant to place threadinterference seal connections into wells requiring more critical levelsof service. Some operators prefer connections with multiple, redundantseals for critical wells. Thus, there is a need for a threadedconnection that uses the industry standard thread form with an improved(positive) sealing system.

[0027] There also is a need for a connection for joining togethertubular sections that will help rig personnel recognize when eachconnection is properly made up. There also is a need for a connectionthat can be properly made up even when the box and pin members are sizedat or near the limits of thread tolerances. There also is a need for aconnection with improved leak resistance, that can reduce or minimizethread galling, and that can resist connection parting (jump-out orjump-in). There also is a need for a coupling that provides an enhancedseal without imparting additional radial hoop stresses. Finally, thereis need for a connection that can provide both enhanced leak andrelatively high tensile efficiency with a reduced coupling outsidediameter (special clearance).

SUMMARY OF THE INVENTION

[0028] The present invention solves the above problems and disadvantagesby providing a coupling with an improved sealing system for joiningtogether tubular sections. This invention uses Standard API threadformsin an enhanced coupling body. The coupling also includes an axiallyenergized primary sealing system with a back up thread interferenceseal. The sealing system is unique because it imparts no additional hoopstresses in the connections beyond those needed for the secondary threadinterference seal. This feature allows the connections to be madespecial clearance and provide both enhanced seal-ability and superiorresistance to jump-out. The coupling includes an unthreaded centersection with a seal seat on which the seal assembly is positioned. Theseal assembly includes an elastomeric component and a substantiallyrigid component that limits advancement of the tubular section into thecoupling.

[0029] The coupling and sealing system of the present invention can beused in any threaded tubular connection where effective resistance tohigh liquid or gas pressure is required. While the coupling and sealingsystem described here is presented primarily for oilfield applications,it is also applicable to any threaded, tubular connection requiringhigh-pressure sealing.

[0030] The present invention may be used in conventional API threadedcouplings, other couplings similar in geometry to API couplings, andcouplings with center section enhancements. Thus the invention may beemployed in couplings of U.S. Pat. No. 5,015,017, wherein the couplinghas stop shoulders on each side of an enhanced center section. In acoupling with stop shoulders, the seal assembly is positioned on a sealseat adjacent the stop shoulders on each side if the coupling. Duringmake-up, the seal assembly is compressed axially between the pin facesand the stop shoulders. If the coupling lacks internal shoulders,however, the seal assembly may be positioned on a seal seat adjacent thecenter section of the coupling so that the seal assembly is axiallycompressed during make-up between the opposing pin faces.

DESCRIPTION OF THE DRAWING

[0031]FIG. 1 is a cross section view of the coupling with internalshoulders according to a first preferred embodiment of the presentinvention.

[0032]FIG. 2 is an enlarged view of the internal shoulder and seal seataccording to a first preferred embodiment of the present invention.

[0033]FIG. 2A is an enlarged view of the seal seat according to a firstpreferred embodiment of the present invention.

[0034]FIG. 3 is a cross section view of an un-shouldered couplingaccording to a second preferred embodiment of the present invention.

[0035]FIG. 4 is a cross section view of the seal insert according to apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0036] As shown in FIG. 1, a first preferred embodiment of the presentinvention includes tubular sections 11, 12 connected together withcoupling 13. In FIG. 1, tubular section 11 is in the hand tight positionand tubular section 12 is in the power tight position. Each of thetubular sections includes external pin threads 21, 22 which mate withinternal threads on threaded areas 14, 15 of the coupling. The couplinghas a first end 16 and a second end 17.

[0037] In the first preferred embodiment, the pin threads and boxthreads are standard API threads, and most preferably API buttressthreads. The present invention, however, may be used with threadedtubular connections having various other thread forms.

[0038] In the embodiment of FIG. 1, center section 18 is located axiallybetween ends 16, 17 of coupling 13. Axial refers to the longitudinalaxis of the coupling and tubular sections. The center section of thecoupling is between the threaded areas. The center section isunthreaded, has increased thickness, and includes first stop shoulder31, second stop shoulder 32, and annular interior surface 33therebetween. The inside diameter of the center section is approximatelyequal to the inside diameter of each of the threaded tubular sections,and is preferably not less than the inside diameter of each threadedtubular section.

[0039] Threaded areas 14, 15 of the coupling terminate at thread reliefgrooves 41, 42. Adjacent the thread relief grooves are shoulders 31, 32.Adjacent the shoulders are seal seats 35, 36. Each seal seat isdimensioned to have a seat width and seat diameter sufficient to holdseal assembly 60 thereon, and preferably includes a snap surface 37(shown in FIG. 2) which provides an abutment or other seal retainingmeans to retain and lock the seal assembly on the seal seat adjacent theshoulder. Upon separation of each of the threaded tubular sections fromthe coupling, each of the seal assemblies are retained with thecoupling. In a 7⅝ inch outside diameter coupling, each snap surface 37preferably has an internal diameter 0.005 inches less than the internaldiameter of seal seats 35, 36, and preferably a width of 0.0125 inches.The internal diameter of the snap surface is preferably slightly lessthan the diameter of the outer perimeter of the seal assembly.

[0040] The seal seat of the present invention is located in theunthreaded area of the coupling inside diameter. In a coupling with acenter section having stop shoulders, as shown in FIG. 1, each seal seatis adjacent a stop shoulder. In the hand tight position, the pin face51, 52 of each tubular section reaches an axial position at or near theseal seat.

[0041] Now referring to FIG. 3, coupling 101 is shown according to asecond preferred embodiment without a center section and without stopshoulders. Seal seat 102 is positioned in the center of the coupling,axially between the pin faces of the two tubular sections. Tubularsection 105 is in the hand tight position, and tubular section 106 is inthe power tight position. Pin face 103 is adjacent the seal seat and pinface 104 abuts the seal assembly.

[0042] In both of the preferred embodiments, as the tubular sectionaxially advances from the hand tight to the power tight position, thetubular section abuts the seal assembly on the seal seat and compressesthe seal assembly axially as will be described in more detail below.

[0043] Seal assembly 60 of the present invention also may be referred toas a gasket or gasket assembly. As shown in FIG. 4, in a preferredembodiment, seal assembly 60 is removable from the coupling and includesa rigid annular retainer 61 and a pair of annular seal elements 62, 63,each seal element supported on a corresponding side of the retainer.When the seal assembly is positioned on the seal seat and is compressedaxially between the pin face and stop shoulder, or between opposing pinfaces, the seal elements are compressed affecting a fluid (liquid orgas) tight seal.

[0044] The retainer in the seal assembly has inner perimeter 64 andouter perimeter 65. The outer perimeter of the retainer is dimensionedwith the same diameter as the seal seat, or slightly less than the sealseat diameter for ease of assembly. The inner perimeter of the retaineris dimensioned to have the same or slightly smaller diameter than thecenter section of the coupling and/or the pin face. In a preferredembodiment of the coupling for joining nominal 7⅝ inch outside diametertubular sections, the coupling center section has an inside diameter of6.765 inches and the seat diameter is 7.325 inches. In this embodiment,the outer perimeter of the retainer has a diameter no greater than 7.325inches and the inside perimeter of the retainer is 6.765 inches or less.Preferably, annular elastomeric locating member 66 is affixed to theouter perimeter of the retainer. The elastomeric locating member mayhave an interference fit with the seat diameter if desired. The annularelastomeric locating member has an outer diameter slightly larger thanthe diameter of the snap surface, so that the seal assembly is held inposition on the seal seat.

[0045] The retainer of the present invention provides a positive stop tolimit axial travel of the threaded tubular section and limit axialcompression of the seal assembly. In a preferred embodiment, theretainer is made from a metal, although plastic or other rigid orsubstantially rigid material also may be used. The retainer has radialsurfaces 67, 68 defining the axial thickness of the retainer. The axialthickness of the retainer is dimensioned to be the same as the seal seatwidth, or slightly less than the seal seat width for ease of assembly.In a preferred embodiment of the coupling for joining nominal 7⅝ inchoutside diameter tubular sections, the seal seat width is 0.150 inches.Thus, the axial thickness of the retainer is no more than 0.150 inches.The seal seat and retainer dimensions depend on the intended applicationof the present invention. However, the retainer in the seal assemblyshould be generally rigid or substantially rigid to limit the axialcompression of the seal elements and to provide a specific and knownclearance between the pin face and stop shoulder in the power tightposition. The retainer should be substantially rigid so that any furtheraxial advancement of the threaded tubular section into the coupling willnot occur without application of additional and excessive torque. Theretainer also is provided with a pair of mounting grooves 71, 72, eachmounting groove on one of the radial surfaces thereof. Each groove is agenerally U-shaped channel in the radial surface of the retainer.

[0046] In a preferred embodiment, each seal element of the seal assemblyis positioned in a mounting groove in the retainer. Each seal elementhas an annular shape formed of an elastomeric material such as syntheticrubber or various other resilient materials that are capable ofretaining their shape and resiliency after deformation. The seal elementhas an inside perimeter 80 with a diameter greater than the diameter ofthe inside perimeter 64 of the retainer and an outside perimeter 88 witha diameter less than the diameter of the outside perimeter 65 of theretainer. The first surface 74 of each seal element is dimensioned tofit in each retainer mounting groove, and may be adhesively bonded,chemically bonded or otherwise attached to the retainer mounting grooveif desired. The second surface of each seal element has a channel 77, 78adjacent the inside perimeter 80 of the seal element and a lobe or beadportion 75, 76 adjacent the outer perimeter of the seal element. Thelobe or bead extends or protrudes axially from the radial surface of theretainer such that the lobe or bead portion comes into contact with thepin face before contacting any other part of the seal assembly.

[0047] Axial advancement of the tubular section into the couplingresults in elastic deformation of the lobe portion of the seal until thepin face abuts the retainer. The lobe or bead portion of the sealprovides sealing engagement with the pin face. Thus, the seal element ofthe seal assembly is axially compressible and the retainer is thecomponent limiting axial compression of the seal assembly. The retaineralso may provide a metal to metal seal with the pin face and shoulder orbetween opposing pin faces. By limiting the axial compression of theseal assembly, damage to the seal elements during assembly or from theapplication of torque is reduced or minimized.

[0048] The opposing radial surfaces of the retainer are provided with aplurality of channels 93, 94 therein between the groove and the inner orouter perimeter of the retainer. The channels provide a path for ventingof fluid, thread compound or other liquid that may be trapped betweenthe shoulder and pin face, and that would reduce the effectiveness ofthe seal assembly.

[0049] Thus, the metal component, or retainer, limits the axialcompression of the seal elements or elastomeric components of the sealassembly. Preferably, each elastomeric component has an interfit withthe retainer such that at least part of the elastomeric component iscompressed. The resilient elastomeric component protrudes axially fromthe metal seal component. During assembly of the tubular sections intothe coupling, the face of the pin initially engages the protrudingportion of the elastomeric seal component during axial advancement ofthe pin into the box. As the pin continues advancement to shouldering,the elastomeric component is further compressed axially, energizing theresilient elastomeric seal and then forming a metal-to-metal seal withthe pin face.

[0050] At completion of make-up, the elastomeric seal element is theprimary sealing mechanism in the coupling, backed up by themetal-to-metal seal. Under extreme load cases, particularly tension, themetal seal may lose contact pressure with the pin face. In these extremeload conditions the elastomeric seal will maintain leak integrity of theconnection. If desired, both of the seal assembly components also may bebacked up by an enhanced thread interference seal as described in U.S.Pat. No. 5,015,017.

[0051] With the present invention, neither the primary elastomeric sealnor the secondary metal-to-metal seal impart hoop stresses in thecoupling. This is an advantage over the prior art couplings havingsealing mechanisms that impart hoop stresses into the box member throughthe use of elastomeric seal rings within mating thread elements and/orcouplings that imparted additional radial hoop stresses in the boxmember when energized by the application of torque during make-up.

[0052] The present invention also eliminates the imposition ofadditional hydraulically induced hoop stresses in the connection due totrapped thread compound. Such hydraulically induced hoop stresses can beseriously detrimental to connection performance. Thread relief grooves41 and 42 provide a reservoir for excess thread compound to migrateduring make-up. The elastomeric seal is specially formed to flush excessthread compound toward the pipe ID as it compresses. Channels 93 and 94provide channels allowing flushed compound to flow to the casing ID.These special design provisions eliminate fouling of the elastomericseal by trapped thread compound.

[0053] The present invention also solves the problem of variabilityduring make-up by rig personnel. During make-up, the pin axiallyadvances until its nose engages the retainer and drives it into theinternal stop shoulder of the box and stops. For connections withoutstop shoulders the pin axially advances until its nose engages theretainer and drives it into the opposing pin member. Rig personnel caninstantly recognize proper make-up when the seal is formed between thepin nose, seal assembly, and stop shoulder or between the opposing pinnoses.

[0054] The present invention has been described and illustrated withrespect to specific embodiments. It will be understood to those skilledin the art that changes and modifications may be made without departingfrom the spirit and scope of the invention as set forth in the appendedclaims.

What is claimed is:
 1. A coupling for joining together threaded tubularsections, the coupling having opposing first and second internallythreaded end sections, comprising: (a) at least one seal seat positionedbetween the first internally threaded end section and the secondinternally threaded end section; and (b) a removable seal assemblypositioned on the seal seat, the seal assembly having an elastomericcomponent and a substantially rigid component, the elastomeric componentbeing resilient and protruding axially from the substantially rigidcomponent, the elastomeric component being axially compressible by atleast one of the internally threaded end sections, the substantiallyrigid component limiting axial compression of the elastomeric componentof the seal assembly and limiting the axial advancement of at least oneof the internally threaded end sections.
 2. The coupling of claim 1further comprising a plurality of channels in the rigid component of theseal insert.
 3. The coupling of claim 1 further comprising a snapsurface adjacent the seal seat.
 4. The coupling of claim 1 wherein therigid component of the seal assembly has an outer perimeter and innerperimeter, and the seal seat has a diameter greater than the diameter ofthe outer perimeter of the rigid component.
 5. The coupling of claim 4wherein the coupling has a center section with an internal diametersmaller than the internal diameter of the first and second internallythreaded end sections.
 6. The coupling of claim 5 wherein the centersection has opposing first and second shoulders and a seal seat adjacenteach of the first and second shoulders.
 7. A coupling for joiningtogether threaded tubular sections, each threaded tubular section havingexternal threads, comprising: (a) first and second internally threadedend sections, each end section having an internally tapered threadedarea beginning at the outer end of the end section and terminating at athread relief groove, the first and second end sections joined togetherto form an unthreaded intermediate area; (b) a seal seat in theunthreaded intermediate area, the seal seat having an internal diameterless than the internal diameter of the threaded areas; and (c) a sealassembly configured to fit on the seal seat, the seal assembly having arigid component retaining at least one elastomeric seal element, theelastomeric seal element forming a seal with the end of a threadedtubular section by application of axial force against the seal element.8. The coupling of claim 7 wherein the end of the threaded tubularsection engages the elastomeric seal element before engaging the rigidcomponent of the seal assembly.
 9. The coupling of claim 7 wherein therigid component limits axial compression of the elastomeric sealelement.
 10. The coupling of claim 7 wherein the threaded tubularsection forms a metal-to-metal axial seal with the rigid component. 11.The coupling of claim 7 wherein the coupling includes a snap surface forretaining the seal assembly on the seal seat.
 12. The coupling of claim7 wherein the seal assembly includes at least one channel in the outersurface of the rigid component.
 13. An improved coupling for repeatedlyjoining together externally threaded tubular sections, comprising: (a)first and second internally threaded ends and an unthreaded intermediatesection axially spaced between the first and second internally threadedends; and (b) at least one seal assembly seated on a seal seat in theintermediate section and spaced axially between the first and secondinternally threaded ends, the seal assembly having an axiallycompressible resilient component and a substantially rigid component,the resilient component of the seal assembly forming a seal with the endof a threaded tubular section and the substantially rigid componentlimiting axial advancement of the externally threaded tubular sectioninto the coupling.
 14. The improved coupling of claim 13 wherein therigid component comprises a metal retainer.
 15. The improved coupling ofclaim 13 wherein the axially compressible resilient component protrudesaxially from the rigid component.
 16. The improved coupling of claim 13further comprising a pair of axially compressible resilient components.17. The improved coupling of claim 13 wherein the unthreadedintermediate section has internal shoulders and an inner diametersubstantially the same as the inner diameter of the externally threadedtubular sections.
 18. The improved coupling of claim 13 comprising apair of seal assemblies, each seal assembly engaging the end of one ofthe externally threaded tubular sections.
 19. The improved coupling ofclaim 13 further comprising a snap ridge for retaining the seal assemblyin place on the seal seat.
 20. The improved coupling of claim 13 whereinthe coupling and threaded tubular sections have API threads.